QuickMail is the best, and easiest, way to send an email to your class or to an individual student inside Moodle. The QuickMail block (see picture at right) is accessible from the main page of your course shell. Click on Compose New Email to select any or all of your students to receive an email.
QuickMail keeps a record of all your emails to students (just click on View History). It allows attachments, and also allows you to keep a set of email signatures from which you can choose for each email. Messages are sent to the students' email addresses, and replies will come to your email address.
For instructions on how to use QuickMail, see the see Learning House's Knowlegebase article here.